Paper shredder with allowable thickness warning function

A paper shredder with an allowable thickness warning function for cutting plural papers, said paper shredder comprising:

• a casing;
• an input tray disposed on said casing for placing said plural papers thereon;
• a shredding entrance disposed in said casing and located at a bottom of said input tray, wherein said plural papers on said input tray are introduced into said casing through said shredding entrance;
• an upper cover disposed over said casing, and rotatable relative to said casing;
• a pressing member disposed on a bottom of said upper cover and movable upwardly and downwardly relative to said upper cover, wherein when said upper cover is rotated relative to said casing to cover said casing, said pressing member is contacted with said plural papers on said input tray and said pressing member is pushed by said plural papers;
• and
• a thickness detecting device disposed within said upper cover and located near said pressing member, wherein if an overall thickness of said plural papers exceeds an allowable thickness, said pressing member is pushed by said plural papers, so that said thickness detecting device is triggered by said pressing member to generate a warning signal.